The present invention relates to a method for correcting out-of-flatness of a rolled material such as a steel strip and a sheet.
The out-of-flatness of a rolled material such as a steel strip as hot rolled may be classified roughly into shape defect and warp. The shape defect is due to a difference in longitudinal elongation of the material and cannot be corrected unless a plastic elongation is provided thereto.
Heretofore, a roller leveler has been used to correct a warp and to reduce a residual stress in the rolled material. A typical roller leveler heretofore used comprises a pair of pinch rolls disposed on the entrance side for the material and a plurality of leveler rolls disposed zigzag in succession to the pinch rolls. The pinch rolls are driven by a motor and the leveler rolls are driven simultaneously by another motor through a gear box. The pinch rolls and the leveler rolls may be driven commonly by the same motor.
The pinch rolls send the material into the leveler and are disposed, in a reciprocating leveler, on the entrance and exit side of the leveler rolls. The pinch rolls have a small load and the same material feed speed as the leveler rolls. Accordingly, it was impossible for the conventional pinch rolls to provide a plastic elongation to the material during leveling.
The leveler rolls are supported usually by several trains of back-up rolls and compensated for in deflection. The leveling intermesh (the quantity of relative setting of the upper and the lower rolls) can be established on the entrance and the exit sides independently from each other. Leveling is performed with tilting.
However, the conventional roller levelers have a low capacity for correcting shape defects since they are designed to correct warps (particularly, longitudinal warp) and to reduce residual stresses. In order to provide a plastic elongation to the material with the roller leveler, it is necessary to provide an axial force positively. The conventional roller leveler is not capable of providing the plastic elongation and is low in the capacity of correcting shape defects because it is only the residual stress in the material and the frictional force between the roll and the material that act as the axial force.
Further, in the rolled material such as a steel strip, a camber bending greatly in the longitudinal direction is produced. The principle of correction of the camber is to provide the material with a larger elongation in the curved inside than in the outside or to provide the material with a bending in the direction opposite to the camber by changing the direction of movement of the material. In the conventional roller leveler, however, it is impossible to change the curvatures of the inside and the outside of the material during leveling, since the leveler rolls are disposed at right angles to the longitudinal direction of the material and, accordingly, are not inclinable in the horizontal or vertical planes. Therefore, it is almost impossible in the conventional roller leveler to correct the camber during leveling.